This invention relates to conveyance of a long sheet-like subject (hereinafter simply referred to as the “sheet”). More specifically, this invention relates to a conveying unit capable of reducing damage to a sheet due to friction or other defect and a vacuum deposition device employing such conveying means.
Various functional films (functional sheets) including gas barrier films, protective films, and optical films such as optical filters and antireflection films are used in various devices including optical devices, display devices such as liquid crystal displays and organic EL displays, semiconductor devices, and thin film solar batteries.
These functional films have been formed by film formation (thin film formation) through vacuum deposition techniques such as sputtering and plasma CVD.
Continuous deposition of a film on a long strip of substrate is preferable for efficient film formation with high productivity.
A typical device known in the art for conducting such film formation is a roll-to-roll film deposition device using a feed roll having a long strip of substrate (a web of substrate) wound into a roll and a take-up roll in which the substrate having a film formed thereon is wound into a roll. This roll-to-roll film deposition device continuously forms a film on a long strip of substrate in the film deposition chamber while conveying the substrate from the feed roll to the take-up roll along a predetermined pathway passing through the film deposition chamber where the film is formed on the substrate by plasma CVD. In this device, the substrate is fed from the feed roll in synchronism with the winding of the substrate having the film formed thereon on the take-up roll.
Rollers are used to convey a long sheet not only in such a roll-to-roll film deposition device but also in a device for winding a produced plastic film and a device for producing a magnetic recording medium.
As a matter of course, conveyor means such as a roller is required to convey a sheet without causing damage thereto. However, differences between the rotational speed of the roller and the speed of a sheet due to variations in the rotational speed and conveying speed and variations in the tension of the sheet cause the sheet to come in sliding contact with the roller, which may cause damage to the sheet such as scratches on the sheet surface. In cases where the sheet has a flexible organic film formed on its surface, the pressing force with which the roller presses the sheet may cause damage to the sheet to deteriorate its surface properties.
In the case of, for example, an optical film, the damage to the sheet and the deterioration of the surface properties may cause light to diffuse or scatter and the resulting product will not proper.
If a sheet has damage to its surface or deteriorated surface properties in forming a film on the surface of the sheet by vacuum deposition, proper crystal growth is hindered, making it impossible to deposit a thin film having desired properties, further causing cracks and missing parts in the thin film. As a result, in producing a functional film such as a gas barrier film having a gas barrier layer formed by vacuum deposition or an antireflection film having an antireflection layer formed by vacuum deposition, the resulting product cannot have desired performance, thus leading to a decrease in the yield.
In order to solve such problems, various means for conveying sheets have been proposed.
For example, JP 2000-86032 A discloses a roller (film conveyor roll) which is hollow and has a large number of through holes formed at the peripheral surface of the roller so that air is discharged from the inside of the roller to the outside and which prevents damage to a sheet due to the roller by conveying the sheet in a state in which it is floated from the roller by the discharged air.
A stepped roller is also known which has large-diameter portions at both ends and conveys a sheet with its both ends in the width direction (direction perpendicular to the direction in which the sheet is conveyed) supported by the large-diameter portions.